Motor graders have a longitudinal main frame which has a dirigible wheel assembly at its forward end, an operator's cab at its rearward end portion, and a traction chassis for the motor and power train behind the cab. The motor grader blade is suspended from the main frame by means of a circle draw bar and a circle. The circle draw bar has its front end connected to the front of the main frame by a ball and socket connection, while the rearward portion of the circle draw bar is suspended from the main frame by hydraulic cylinder and piston means which permit the draw bar to swing in a vertical plane about its front end.
The circle is mounted on the rearward portion of the circle draw bar for rotation about a vertical axis, and there is a driving interconnection between a motor on the circle draw bar and a ring gear on the circle to effect such rotary motion of the circle.
The grader blade is mounted upon the circle so that rotation of the circle changes the angle of the blade with reference to the path of travel of the grader, while swinging the circle draw bar in a vertical plane about its forward end changes the vertical position of the grader blade with reference to the ground.
In addition, the grader blade is mounted on a horizontal axis so that it may be tipped with respect to the circle by hydraulic cylinder and piston means to change the angle of attack of the blade and it may also be shifted endwise in its mounting.
While the grader blade must be mounted for tilting movement and for lateral shifting movement as above described, it is essential that in operation the blade be securely locked against movement. Surface tolerance requirements are becoming increasingly restricted both in highway construction and in the preparation of other construction sites where concrete is to be laid on the ground. Thus, for example, the minimum thickness of concrete in a road must be maintained for the proper strength, which requires an accurate subgrade. Present day grading tolerances for such work may restrict subgrade surface variations to a small fraction of an inch. This, of course, requires very accurate locking of the blade in any desired working position.
Further, the lock and the blade must cooperate in such a way that releasing the lock to permit side shifting of the blade does not permit the blade to shift in its mounting and thus cause a variation in the graded surface.
The most pertinent prior art of which applicant is aware is disclosed in U.S. Pat. No. 3,593,806.